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AB Systems 410a

S

splatee

New Member
Hello,

I just acquired a AB Systems 410a and have a few questions. First thank you to Bob over at AB International for emailing me a copy of the service manual for it. Now going through the service manual it says to set D.C. Offset and bias using a 1k hz sign wave at 1w. Now I do not have signwave generator or a power supply, is there any other way to set these? I have set bias and D.C. Offset on Hafler and Kenwood amplifiers using volt meter. Also I need to look at the power switch because it does not turn the amplifier off. I am gong to be using the amp for subwoofer duty.

Thank you
 
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Ok I measured the DC offset voltage and this is what it read.

Channel 1 = 209mV
Channel 2 = 45mV

Looking through the manual I am not sure how to adjust it. The top board is accessible but the bottom is not. What would I need to do exactly to lower channel 1?

Also looking at the top board there is a capacitor going across what would be connections for a "bridge" mode switch. I do not see this indicated in the schematics.

Thank you
 

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I was working on a model 410C a little while ago and I can understand your frustration, there were several versions of the 410, obtaining the right information on these 35 year old amps is not easy . I dont know if you seen this procedure but it may be helpful.
Your model may use the power switch to fire a triac which may have shorted rendering it in a constant on state.
ab410.JPG
 
My board layout looks like this one.

So I take it i would adjust the DC Offset using the multimeter on the speaker output and adjust using the the pot to the left? I also jus picked up bipolar caps to replace the ones on the board.
 

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splatee said:
My board layout looks like this one.

So I take it i would adjust the DC Offset using the multimeter on the speaker output and adjust using the the pot to the left? I also jus picked up bipolar caps to replace the ones on the board.
Click to expand...

That would be my guess. All the offset measurements and adjustments that I ever made were with the amp in an idle state, I dont see where a 1khz signal @ 1 watt comes into play.
Getting access to the bottom board is easy enough by removing the screws holding the output transistor assembly to the heat sink
 
Michael F said:
That would be my guess. All the offset measurements and adjustments that I ever made were with the amp in an idle state, I dont see where a 1khz signal @ 1 watt comes into play.
Getting access to the bottom board is easy enough by removing the screws holding the output transistor assembly to the heat sink
Click to expand...

Thank you for the info,

I already have taken the back off of the amp and getting ready to replace the capacitors. Good thing I took a real good look because they are bipolar caps.
 
Just finished up replacing the capacitors on the amp boards and adjusted the DC offset. The bias voltage was within spec so did not touch those. The power cord was replaced also because the original was brittle and falling apart. I didn't not attempt to diagnose the constant on state of the amplifier, I will look at that next time and for now will power it on and off with a power strip.

Thank you
 
Hello
In the end I found something about this amplifier that until now I did not know nor did I find anything about it as to guide me in terms of its brand, model and others

I would be very grateful if you shared a copy of the service manual by this means or to my mail (d-l-o33@hotmail.com)
I have many doubts with this amplifier, "1" would be the + voltage of the source and its amperage since the amplifier came to my hands with its 2 burned transformers, "2" to the right of the output terminals there is a variable resistance !, what would it be and what would be on the left, which would be for the setting of 0 volts at the output or would it be for the rest current and what would it be? and another point is the terminal that I point out in the image, my question is where do I connect that orange cable? apparently it was working with this cable disconnected! thanks
Thank you
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Thank you
 
Great to find your post Splatee. I acquired a 410. It has a blank front panel, no level adjustments, no LED's. Just the power switch and AB logo. One channel is fine. Testing the DC at the speaker terminals I'm seeing 7.35 VDC on channel one. I've been probing around. Appears all the 2 watt resistors are fine, and assuming one of the TO-3 outputs failed....hard to tell which one if it did in circuit. Do you have any pointers that might help me? The bad board is the upper one which I've allready removed the 4 TIGHT mounting screws on the heatsink to gain access to the bottom of the board. You can email me directly at Davidaldridge8@hotmail.com. THANKS!
 
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